The invention relates to an adjustable casting mould and a device for adjusting the mould surface thereof.
Known casting moulds include on the one hand those in which a sand moulding box is prepared each time a workpiece is cast. These sand moulding boxes are well suited for the small-batch manufacture of products. However they have drawbacks concerning the disposal of the used moulding sand. For example, the process of casting four propeller blades for a marine propeller entails 80 m3 of moulding sand which is to be disposed of. These problems can only be partly solved by reprocessing used moulding sand. Reprocessing is also expensive. The preparation of the sand moulding boxes is labour-intensive and time-consuming.
In addition, moulds which can be used many times are known for the large-batch manufacture of castings which are not overlarge. However these casting moulds are very expensive to produce, which means that it is out of the question to use them for small-batch production.
In order to produce a casting mould with an adjustable mould surface, DE 41 12 736 C2 has already proposed rod-shaped moulding pins which can be moved axially relative to one another so as to be clamped together in a frame, with the end faces of the variably adjusted moulding rods predetermining a staircase curve mould surface of adjustable geometry.
One disadvantage of an adjustable casting mould of this kind lies in the fact that the various moulding pins cannot be firmly fixed in position until they have all been brought into the desired axial position. The moulding pins may move under disturbing influences until they are thus fixed. Moreover, the process of fixing the positions of the moulding pins by clamping the entire pack of moulding pins together, in which case they are just fixed through pure frictional engagement, is not without problems: Firstly, the clamping forces under casting conditions may differ considerably from those under adjustment conditions on account of differing thermal expansion of the moulding pins and clamping frame. Secondly, the clamping forces must be cleanly transmitted from one moulding pin to the adjacent moulding pin in the moulding pin pack. This means that the side faces of the moulding pins must lie exactly flat against one another. The moulding pins must therefore be very accurately machined and, if re-used, adequately cleaned. However it is impossible to produce adjustable casting moulds for very large workpieces even if appropriate precautionary measures are observed, as the moulding pinsxe2x80x94which are only held by frictional engagementxe2x80x94cannot take relatively high loads in the axial direction and may move in uncontrolled fashion under the effect of the weight of relatively large quantities of molten metal.
The object of the invention is therefore to develop an adjustable casting mould according to the preamble of claim 1 such that the position of the individual moulding pins is more securely fixed, even if the mould has large dimensions.
This object is achieved according to the invention by an adjustable casting mould.
The individual moulding pins of this mould are each supported by an associated stanchion which is adjustable in length. As each moulding pin has its own support, which is independent of the support of adjacent moulding pins, the concept according to the invention enables casting moulds of any desired size to be produced without any problems.
The concept according to the invention also enables groups of moulding pins to be assembled into sub-units which can be handled and transported without any risk of the adjusted mould parting plane changing, while still ensuring that the mould surface is substantially continuous, so as to be free from joints, after the various moulding pin groups have been positioned side by side.
Advantageous developments of the invention are presented in subclaims.
The use of a screw drive to support the moulding pins is of advantage with regard to a simple, precise adjustment of the end faces of the moulding pins. This adjustment may also be performed in a particularly simple manner by using a robot. A stanchion of this kind, adjustable in length, is also particularly insensitive to high temperatures.
The development of the invention is of advantage with regard to a good, reliable alignment of the moulding pins irrespective of their axial position.
The development of the invention ensures that the screw drive which is used to adjust a moulding pin is protected against high temperatures under casting conditions.
If the threaded hole or spindle nut of the screw drive is provided on the guide section, the screw drive can be adjusted particularly easily to the head, which always occupies the same axial position, of the adjusting bolt.
The development of the invention has the advantage of the position of the mould surface not changing significantly if the temperature prevailing during the casting operation differs from the temperature which was taken as a basis when predetermining the desired positions for the various moulding pins.
The development of the invention enables the initially stepped mould surface to be converted into a smooth mould surface through mechanical reworking.
The development of the invention enables the material of which the volume of the moulding pins consists to be selected so as to be particularly favourable with regard to its thermal properties or machinability, while still guaranteeing that the moulding pins are mechanically held together as desired. If the sheath is thin, it does not represent a high resistance for the machining tool should any reworking of a stepped mould surface by machining be carried out.
If groups of moulding pins are provided on carrier plates, these groups of moulding pins can be adjusted on easily surveyed, small devices, particularly using automatic machines. The use of groups of carrier plates bearing moulding pins is also of advantage with regard to easily fastening the moulding pins in the moulding box and with regard to providing moulding boxes of different sizes using uniform basic components. Because the carrier plates are in turn mounted on the frame of the moulding box so as to be adjustable in the axial direction of the moulding pins, it is also unnecessary to provide an excessively long axial displacement path for the individual moulding pins, although it is still possible to produce large castings having different dimensions parallel to the longitudinal axis of the moulding pins.
The development of the invention is of advantage with regard to easily mounting the carrier plates on the moulding box frame such that they can bear loads.
A casting mould enables the individual carrier plates and the moulding pin groups borne by them to be very easily connected to the moulding box frame, in which case the positioning of the moulding pin groups flush side by side automatically takes place in two directions perpendicular to one another (in the first instance through abutment, secondly through the spacing of the rails).
The development of the invention enables sub-regions of the mould surface, in which different demands are made on the variability of the mould surface, to be formed economically. Thus edge regions of the moulding box parting plane, which only serve to close the mould cavity, can in the extreme case simply be closed by carrier plates bearing just one cuboid moulding pin. These moulding pins then only need to be adjusted to the mould parting plane, this being the only adjustment operation required. Carrier plates which are provided with sprue channels and vent channels may then also be mounted in such edge regions of the moulding box.
The development of the invention is also of advantage with regard to easily introducing the moulding pins into the moulding box and easily removing them from the latter again.
The development of the invention enables the temperature at the moulding box frame and therefore at the mechanism for suspending and bearing the moulding pins to be maintained at a low level.
A casting mould has a substantially smooth mould surface. Where large casting moulds are concerned, the end faces of the moulding pins are preferably machined after the axial position of the moulding pins of a carrier plate has been adjusted in each case separately for such a moulding pin group. CNC machines with long traversing paths are therefore unnecessary. However, where such machines are available, it is also possible to rework the stepped surfaces formed by the moulding pin end faces to form a mould surface which is smooth throughout at the actual casting mould.
An uninterrupted mould surface can also be achieved by smearing the stepped surface formed by the moulding pin end faces with a heat-resistant mouldable material, whereby a substantially continuous mould surface is likewise obtained. If a casting mould thus smeared is re-adjusted, the moulding material applied to the end faces of the moulding pins will generally separate automatically if the moulding pins are displaced unequally. This may be further assisted by spraying the moulding pin end faces with a parting compound before the mouldable material is applied.
The development of the invention is of advantage with regard to minimising the weight of the moulding pins and/or their displacement mechanism, which facilitates handling of the moulding pins and entire moulding pin groups. If an end section of the moulding pins remains solid in this case, it is also possible to machine the end faces of such moulding pins to produce a continuous mould surface.
The development of the invention enables the end faces of the individual moulding pins to be automatically adjusted to the desired mould surface. This is of advantage in particular where very large moulds are concerned and for the frequently varying manufacture of different products.